A four-joint link mechanism type stepless transmission has been conventionally known. The four-joint link mechanism type stepless transmission includes: an input shaft to which a drive force from a drive source such as an engine provided in a vehicle is transmitted; an output shaft disposed in parallel with the input shaft; a plurality of rotational radius adjusting mechanisms provided on the input shaft; a plurality of swing links pivotally supported by the output shaft to be swingable; and connecting rods each of which has one end provided with an input-side annular section externally fitted to the corresponding rotational radius adjusting mechanism to be rotatable and the other end connected to the swing end of the corresponding swing link (for example, see Japanese Translation of PCT International Application Publication No. 2005-502543, hereinafter referred to as Patent Literature 1).
In the stepless transmission in Patent Literature 1, each rotational radius adjusting mechanism includes: a discoid cam portion eccentric with respect to the input shaft; a rotary portion eccentric with respect to the cam portion to be rotatable; and a pinion shaft. A one-way clutch is provided between the swing link and the output shaft. The one-way clutch locks the swing link to the output shaft when the swing link starts to relatively rotate to one side with respect to the output shaft, and lets the swing link idle with respect to the output shaft when the swing link starts to relatively rotate to the other side.
Each cam portion has: a through hole in the axial direction of the input shaft; and a cutout hole that is formed at a position opposite to the eccentric direction with respect to the input shaft and provides communication between the outer peripheral surface of the cam portion and the through hole. The cutout hole is formed from one end surface in the axial direction of the cam portion to the other end surface. Adjacent cam portions are fixed by bolts, thus constituting a cam portion connected body. One end of the cam portion connected body in the axial direction is connected to the input shaft, and the cam portion connected body and the input shaft constitute a cam shaft.
The cam portion connected body is hollow as the through holes of the respective cam portions are linked together, and the pinion shaft is inserted therein. The inserted pinion shaft is exposed through the cutout hole of each cam portion. The rotary portion has a receiving hole for receiving the cam shaft. Internal teeth are formed on the inner peripheral surface of the rotary portion defining the receiving hole.
The internal teeth mesh with the pinion shaft exposed through the cutout hole of the cam shaft. Rotating the input shaft and the pinion shaft at the same speed maintains the radius of the rotational motion of the input shaft by the rotational radius adjusting mechanism. Setting the input shaft and the pinion shaft at different rotational speeds from each other changes the radius of the rotational motion of the input shaft by the rotational radius adjusting mechanism, thus changing the transmission gear ratio.
Rotating the input shaft so as to rotate the rotational radius adjusting mechanism causes the input-side annular section of the connecting rod to carry out rotational motion, as a result of which the swing end of the swing link connected to the other end of the connecting rod swings. In other words, the rotational radius adjusting mechanism, the connecting rod, and the swing link constitute a lever crank mechanism. The swing link is provided around the output shaft via the one-way clutch, so that the swing link transmits a rotational drive force (torque) to the output shaft only when rotating to one side.
The eccentric directions of the cam portions of the respective rotational radius adjusting mechanisms are set so that the cam portions have different phases to form a circle around the input shaft. The connecting rods externally fitted to the respective rotational radius adjusting mechanisms cause the swing links to transmit torques to the output shaft in order, enabling smooth rotation of the output shaft.